Costs originating from government policies that are passed along to the public hit the little guy hardest. A boost in the light bill can be shrugged off by someone making $100,000, but not for the $25,000 earner. A coal-industry study, admittedly self-serving but hardly challengeable, says that energy takes nearly a quarter of the budget of a household earning $20,000 to $30,000 but less than 10% of a $50,000 income. Mr. Obama’s war on fossil fuels has sent energy costs up.

Another study, published in Public Finance Review in 2004, zeroed in on counties that lie along state borders. Because territories in such close proximity often share characteristics that might not be captured in other measurements, this is a promising approach for isolating the effects of state policy. Studying 30 years of data, the authors concluded that states that raised their income tax rates more than their neighbors had significantly slower growth rates in per-capita income.

Similarly, economists Brian Goff, Alex Lebedinsky, and Stephen Lile of Western Kentucky University grouped pairs of states together based on common characteristics of geography and culture. This is the economic equivalent of studying identical twins to probe the relative importance of genetics and environment. Writing in the April 2011 issue of Contemporary Economic Policy, the authors found “strong support for the idea that lower tax burdens tend to lead to higher levels of economic growth.”